This invention relates generally to high-temperature components for gas turbine engines and more particularly to turbine airfoils.
Thermal and mechanical loads applied to the leading and trailing edges and tips of a gas turbine engine airfoil can adversely affect the airfoil's useful life. Airfoils in gas turbine engines experience durability problems at the tip of the airfoil in the form of cracking due to thermally induced stress and material loss due to oxidation and rubbing. This can be addressed by using an alloy having increased resistance to environmental oxidation and corrosion. However, it is undesirable to upgrade the entire airfoil to a more thermal-resistant and oxidation-resistant alloy because this increases component cost and perhaps weight.
Materials having better high temperature properties than conventional superalloys are available. However, their increased density and cost relative to conventional superalloys discourages their use for the manufacture of complete gas turbine components, so they are typically used as coatings or as small portions of components. These highly environmentally resistant materials have proven difficult to attach to the basic airfoil alloys due to a mismatch in liquidus and solidus temperatures between the environmentally resistant alloys (higher liquidus and solidus) and the component alloys (lower liquidus and solidus). This mismatch is great enough that by the time the solidus of the environmentally resistant alloy is reached the liquidus temperature of the component alloy is far exceeded resulting in a melt away of the component. In processes to date that do join the blade alloy to the tip alloy a distinct centerline is formed in the joint. Experience predicts that this type of joint is likely to fail in either fatigue or rupture.
Accordingly, there is a need for a method of attaching environmentally resistant alloys to conventional superalloys.